Quick Reply - You get a text message and you want to quickly reply to it. Instead of getting out of a game or Safari or any other application you're in, you can hit "Reply" and you can reply to the message on the screen. You can even do this in your lockscreen. In order to not swipe to get to the "Reply" option, open up your biteSMS and click on the setting icon in the top right corner (get out of any message you're in). Go to where you see "Quick Reply". Then, "Configure Buttons". You are able to reorder the buttons. My layout for the first three is Later, Open, and Send (the Send will be a Reply).
Quick Compose - First of all, I use Activator and set swiping the status bar down to open a quick compose. This is when you want to send a message to someone, but not necessarily a reply. You put the recipient first (which searches through your address book, or you can look through your favorites), and type a message. You can configure the buttons for Quick Compose as well as I mentioned in Quick Reply.